This invention relates generally to an air filtering arrangement which can be applied to many different devices which have to operate in an atmosphere which contains foreign matter, such as dust, chaff, short straw particles, etc. and in which air from this atmosphere has to pass through relatively small openings in an element of the filtering arrangement to hold back this foreign matter and, more particularly, to a mechanism for cleaning the foreign matter from the external surface of the filtering element to prevent the openings from being blocked.
Such an air filtering arrangement can, for example, be used with cooling devices for combustion engines or hydraulic equipment particularly in conjunction with cooling devices for the combustion engines on harvesting machines, such as combine harvesters. These machines normally work in a very dusty atmosphere as they can only harvest efficiently when the crop is ripe and dry which causes during operation, a considerable amount of dust, chaff and short straw particles to be displaced in the vicinity of the machine. While the use of a filter element prevents this foreign matter from reaching the device being cooled, such as the radiator through which the coolant for a combustion engine flows, it is necessary to prevent that same foreign matter from blocking the filter element itself and thereby interrupting the flow of air to the cooling device and causing overheating.
Known prior art, such as U.S. Pat. No. 407,949, provides an air filter having a filter element through which air is drawn by a first fan, and a second fan for blowing air into an air box which itself has an elongated outlet directing air into the interior of the filter element in a direction opposite to the direction of flow of air which the first fan draws through the filter element to blow away any foreign matter which has collected thereon. This known arrangement is relatively cumbersome in routing the cleaning air through the interior of the filter and furthermore, suffers from the disadvantage that foreign matter blown from the filter element, is discharged generally in the region of the filter element such that it tends to be immediately redeposited on the filter element by the flow of air drawn through the latter by the first fan. A similar mechanism is disclosed in U.S. Pat. No. 3,155,473; however, a single fan is provided on the engine block that is being cooled. On the pressure side of this fan, there is provided a collector which allows air under pressure to be collected and transmitted through a duct to the filtering element.
It is also known to remove foreign matter from a rotary filter element by relying solely on gravity and centrifugal forces. Such an arrangement is disclosed in GB-A-No. 1387690. In this arrangement, the filter element is rotatably mounted and on the side thereof opposite to that through which air enters the filter element, there is provided a stationary means such as a plate, which serves to blank off a given area of the filter element as the latter rotates. Thus, any foreign matter collected on the area blanked off by the plate at any given instant is no longer held by the flow of air through the filter element and can thus fall free of the latter under gravity and centrifugal forces.
With this known arrangement as applied to combine harvesters, for example, it has been found desirable to rotate the filter element in a particular given combination at a relatively high rotational speed, such as 450 RPM, in order to achieve satisfactory cleaning. In other words, the faster the rotational speed of the filter element is, the greater the efficiency is in the removal of foreign matter from the filter element. However, the faster the filter element is rotated, the less efficient the filter becomes in allowing cooling air to flow therethrough. Accordingly, the faster the rotational speed of the filter element is, the smaller the cooling effect is of the overall cooling system to which the filter element is fitted. In other words, contradictory requirements exist. To improve the foreign matter removal efficiency, the rotary air filter speed should be increased, while that this same speed should be decreased for improving the cooling efficiency.
While such a rotary air filter of particular dimensions has been found satisfactory with engines of horsepower in the range of 200 HP, it also has been found necessary to improve the overall efficiency of the cooling system without resorting to the obvious expedient of increasing the size of the radiator through which flows the coolant for an internal combination engine of a combine harvester, for example, when higher horsepower engines are used, as is becoming more often the case. Any increase in radiator size not only increases the cost but also presents a problem of finding sufficient room to accomodate such a component.
Similarly, a rotary air filter of larger dimensions possibly could match with the higher engine horse power rates but, in combine harvesters, this has become impractical as insufficient room is available to accomodate such a larger component.